Hey Lori,
I agree! I don't like setting rules, fashion is for everyone and older women can rock many styles that younger girls wear and even can't wear. It all depends on the body shape and the intended look. Mini skirts are not for everyone and I like them mostly as an evening/beach look. If an older woman has a great body she can wear them too. Above the knee is also fine.
As for skinny jeans, if you're comfortable why not? You could also wear heels for sure, they elongate the legs and are for everyone, as long as you don't go too high, which is advice that I give to even the youngest girls.
Have fun with fashion and forget the rules! If you know what looks good go for it.
This article by me can help you adapt runway trends if you think something is a bit hard to wear.